1. Field of the Invention
The present invention relates generally to improved dental compositions for obturating and sealing root canals in a tooth. The compositions contain a mixture of gutta-percha and other components. Methods for filling and sealing root canals using the composition are also provided.
2. Brief Description of the Related Art
The inner portion of a tooth includes a pulp cavity that contains soft living tissue or the “pulp” of the tooth. The pulp includes connective tissue blood vessels that nourish the tooth, and nerve endings. Referring to a tooth in the mandibular jaw, the pulp cavity comprises an upper pulp chamber and root canals that extend downwardly to the apex or apical section of the tooth. In a healthy tooth, the enamel of the tooth is a very hard, calcium-based substance that covers the portion of the tooth seen in the mouth, which is known as the crown. Under the enamel is a hard layer of dentin tissue containing a matrix of minute tubules surrounds and protects the pulp. The enamel covers and protects the dentin in the upper portion (crown) of the tooth. The cementum of the tooth is a thin, mineralized tissue that covers and protects the outer surface of the root in the jaw. Dental decay or caries is typically caused by bacteria accumulating on teeth forming a biofilm (plaque). The plaque biofilm produce acids that dissolve or weaken the enamel, forming caries. When dental caries is found in the enamel portion of the tooth, a dental professional will remove the caries in order to prevent further decay of the tooth. In some instances, the dental caries may be so deep that it penetrates the enamel to the dentin tissue. At this point, the bacteria and other microorganisms can migrate rapidly into the pulp tissue causing infection and inflammation. As a result, abscesses or inflammation may form in the pulp and eventually the periapical tissues surrounding the apex or apical section of the tooth in the jawbone, where the teeth are set. The pulp cavity and surrounding bone and tissue may become exposed to infectious bacteria by actions other than decay such as deep cracks or other traumatic injuries to the tooth. Provided that the dental disease is not too progressive, dental professionals will use root canal treatment procedures to remove the damaged tissue from the tooth and replace it with an inert, biocompatible material.
The root canal system of a tooth is complex and many treatment methods can be used depending upon the condition of the patient and the practitioner. In general, root canal treatment methods first involve drilling an opening in the crown of the tooth to provide access to the pulp. Then, endodontic files are used to thoroughly remove the pulp tissue from the pulp chamber and root canals. The files are also used to shape the canals. Next an irrigant may be used to remove residual debris and the smear layer created by the files. The root canal walls are coated with a sealer and then the canals are filled with an inert filling material. This sealing and filling of the roots ideally prevents bacteria and other microorganisms from re-entering and causing infection of the living tissue surrounding the root tip. As a final step, the pulp chamber and opening in the crown of the tooth are filled with a dental restoration such as a composite material. Preferably a permanent restoration with a synthetic crown of metal or ceramic, perhaps including a post for stability, is placed in the tooth. The permanent restoration is normally fabricated after the root canal procedure.
Gutta-percha is a naturally occurring and synthesized isomer of rubber often used to fill and seal the pulp chamber and root canals. Gutta-percha points having a tapered conical shape can be prepared, and these points can be fitted into the root canal. Such gutta-percha points are advantageous, because the tapered shape of the gutta-percha point means that it can assume the tapered shape created by the endodontic files used in the root canal. Historically, one treatment method involved using cold single cones of gutta-percha. In this method, zinc oxide-eugenol cement sealer was first placed in the root canal. Then a single cone of gutta-percha, without lateral condensation, was fitted into the root canal. Subsequently, a cold lateral condensation technique was developed. This technique involved compressing a series of gutta-percha cones into the root canal. A zinc oxide-eugenol cement sealer also was used in this procedure. The filling would essentially comprise multiple gutta-percha cones tightly pressed together in a matrix of dental cement. While this procedure created a more three-dimensional filling of the root canal system, there were still some disadvantages including the possible occurrence of voids or open spaces in the root canal.
More recently, procedures employing heated gutta-percha have been used. Plasticizing the gutta-percha allows it to flow so that it can move into the minute intra-canal spaces, lateral canals, accessory canals, anastomoses, and other irregularities of the canals. Various thermoplastic heating techniques have been developed. In one technique, an instrument with a cannula containing the gutta-percha is used. The cannula is preheated and the needle of the cannula is inserted into the root canal to a predetermined depth. However, it has been found that one problem with heated gutta-percha is that it flows only a small amount and shrinks upon cooling. Combinations of cold and warm gutta-percha techniques are commonly used.
Another technique uses a metal or plastic carrier coated with a layer of gutta-percha. The carrier includes a metal or plastic shaft with a distal tapered end that extends from a handle. The gutta-percha coated carrier is commonly referred to as an endodontic obturator in the dental field. One example of such an endodontic obturator is available from Dentsply Tulsa Dental Specialties (Tulsa, Okla.) under the brand name, THERMAFIL. In practice, the endodontic obturator is first heated in an oven. This heating step plasticizes the gutta-percha. Then, the heated obturator is inserted into the previously cleaned and shaped root canal. The carrier transports the gutta-percha to the working length of the canal and laterally compacts the gutta-percha into lateral and accessory canals. Once the carrier is stabilized in the canal, the upper handle portion and shaft is severed at a point level to the orifice of the canal using a dental bur or other instrument. The lower portion of the shaft remains in the canal encased in the hardened gutta-percha.
Other known materials can be used for treating root canals. For example, compositions containing hydraulic cement can be used, such as portland cement. In general, portland cement contains a dicalcium silicate, tricalcium silicate and usually calcium aluminate, tetracalcium aluminoferrite, and calcium sulfate. Portland cement is commonly gray, but white versions, with lower iron content are known. The chemical composition and physical properties of such cement compositions must be suitable for dental applications.
For example, Torabinejad et al., U.S. Pat. Nos. 5,769,638 and 5,415,547 disclose methods for sealing root canals and filling tooth cavities using a portland cement composition. In manufacturing the cement, the raw materials are crushed, ground, blended and fired to about 1500° C. After firing the cement clinker is ground, and a small amount of calcium sulfate is added to the cement to control the setting time.
Primus, US Patent Application Publication US2005/0263036 discloses a cement composition that is substantially free from iron oxide and has a calcium oxide content in the range of about 50 to about 75% by weight and a silica content in the range of about 15 to about 25% by weight.
A popular and effective material used in root canal treatment is ProRoot™ MTA root repair material available from Dentsply Tulsa Dental Specialties. ProRoot MTA material has a composition similar to portland cement, with the addition of bismuth oxide. Particularly, the ProRoot MTA material includes particles of tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, calcium sulfate dihydrate, and bismuth oxide. ProRoot MTA material is used in a variety of clinical applications including repairing root canal perforations during root canal therapy; filling root ends; repairing root resorption; and apexification of deciduous teeth with immature open roots.
Although traditional gutta-percha compositions are generally effective in treating root canals, it would be desirable to have a more biocompatible composition. Ideally, the improved gutta-percha composition would promote healing of the bones and tissue surrounding the root canal tips and would enhance the seal against bacterial migration into the root canal. The present invention provides such improved gutta-percha compositions having these desirable properties as well as other beneficial features and advantages.